Add address printing functions

Add address printing functions

printaddr is a simple function implementing "print NULL or address"
idiom.
umoven_or_printaddr is a wrapper around umoven that has the same return
value semantics as umoven but also prints the address when the data
is not going to be fetched (in case of exiting(tcp) && syserror(tcp))
or cannot be fetched (umoven fails).
umove_or_printaddr is a macro wrapper around umoven_or_printaddr that
mirrors umove wrapper around umoven.

* defs.h (printaddr, umoven_or_printaddr): New prototypes.
(umove_or_printaddr): New macro.
* util.c (printaddr, umoven_or_printaddr): New functions.